Method and apparatus for pest deterrence

ABSTRACT

A pest deterrent device attracts the attention of a pest with ultrasonic noise and then produces a series of flashes to drive off the pest. In one embodiment, the device continuously produces ultrasound, changing the ultrasound when a pest is detected. In another embodiment, the device does not produce ultrasound until a pest is detected. In a further embodiment, the flash charging circuit is used to modulate the ultrasound while the flash is operated. In a particular embodiment, four ultrasonic speakers are arranged in a series-parallel configuration with a total capacitance of about 0.2 micro-Farads achieve 120 dB of sound output with a supply voltage of about 12-18 V.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a divisional application of U.S. patent application Ser.No. 09/844,065 filed 26 Apr. 2001, the disclosure of which isincorporated by reference.

STATEMENT AS TO THE RIGHTS TO INVENTION MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

[0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] The present invention relates generally to electronic pestdeterrent devices and more particularly to pest deterrent devices thatemit ultrasound to drive off animals.

[0004] Pests, such as birds, deer, cats, dogs, or rodents among others,can cause significant damage to crops, buildings, stored goods, andlandscaping. A variety of methods and devices have been employed toattempt and reduce the damage caused by pests. Some approaches use ascarecrow or replica of a predator, such as an owl or snake, to scareaway pests. Unfortunately, pests often become accustom to these devicesand they lose their effectiveness.

[0005] Other approaches use noise, such as a series of small explosivedevices linked to a slow-burning fuse, and/or propane guns to scare awaypests. Such methods might be inappropriate in an area where the noisewould be bothersome. Additionally, the pests or pest might becomeaccustomed to the repeating noise.

[0006] Yet other methods use a detector, such as a motion sensor, todetect the presence of a pest and trigger a pest deterrent event, suchas a noise. Many such detectors work automatically, emitting a loudsound or tone when movement is detected. Some pest deterrent devicesavoid disrupting human activity or comfort by generating justultrasound, which is beyond the range of human hearing. However, somepests may still become accustomed to the regular sound, even a fairlyloud regular sound. Another issue is that ultrasonic pest deterrentdevices can consume a fairly large amount of power to produce highlevels of ultrasound. Power consumption is not much of an issue if apower outlet is available, but becomes more of an issue if the deterrentdevice is operating on battery power. Finally, a user might not be ableto tell if the unit is working, i.e. emitting sound, because the soundis above his range of hearing.

[0007] Problems associated with power drain can be compounded if thedetector keeps triggering off of continuous motion of the pest.Similarly, many detectors, such as passive infrared (“PIR”) or Dopplerdetectors provide low outputs that must be amplified to turn onrelatively high-power devices like ultrasound generators. Draw on thepower supply and ground current feedback can affect the operation of thedetector-amplifier circuit, causing unreliable triggering.

[0008] Accordingly, it is desirable to provide an automatic pestdeterrent method and apparatus that more effectively drives off pests.It is further desirable that the apparatus be efficient to allowoperation in remote locations using battery power. It is yet furtherdesirable that the user be able to verify that the unit is providingsound.

SUMMARY OF THE INVENTION

[0009] An efficient pest deterrent device uses a detector that providesa detection signal to a microprocessor. The microprocessor is used todirectly generate ultrasound, as well as control the operation andtiming of the device. For example, the microprocessor can detect if thedevice is operated on line or battery power, and change device operationto conserve power when the device is battery-operated. The device canthus operate in a variety of modes. On line power, the device alternatesbetween two ultrasonic tones until a pest is detected, at which pointthe devices changes the ultrasonic output to a sweeping output. Theultrasonic sweep can be combined with a flash, preferably delayed fromthe onset of the swept signal by about one second. This delay allows theattention of the pest to be drawn to the ultrasound, and the flash tostartle or otherwise drive off the pest. In a further embodiment, thestrobe charging circuit's oscillator signal can be used to amplitudemodulate (“AM”) the ultrasound to create noisy sidebands from highultrasonic down to within the normal range of human hearing. This AMcreates even more disturbing ultrasound and also allows an operator toconveniently verify sonic output but at much lower sound levels than theultrasound.

[0010] In one embodiment, a microprocessor-controlled pest deterrentdevice has a passive infrared sensor that produces a train ofalternating positive and negative pulses that are buffered andamplified. The microprocessor is programmed to initiate pest deterrentsignals, i.e. activate a load, when an input voltage signal of aselected polarity rises above a threshold level. The load is not activewhen the input is below the threshold or of the opposite polarity. Theinput signal is provided to the microprocessor by an amplifier and isfed back through a coupling capacitor as positive feedback to the inputof the operational amplifier, which saturates the operational amplifier.After a selected period of time, the capacitor charges and causes aninverse input signal fed back to the input through the same couplingcapacitor, which turns off the load after a selected period of time.

[0011] The operational amplifier then saturates to the opposite rail.Again, the output is coupled through the coupling capacitor as positivefeedback causing the capacitor to discharge. During this selecteddischarge period, the load is off and the activation circuitry will nottrigger off of a pulse from the sensor or other signal, in other words,the sensor is locked out because the input to the microprocessor is ofthe wrong polarity for activating the load.

[0012] In a particular embodiment, the pest deterrent device includesboth a strobe light and ultrasonic speakers. When a pest is detected,the device either initiates ultrasound or changes the ultrasonic output.After a selected period of time, which can be programmed in themicroprocessor, the strobe is activated and flashes several times for abrief period and then remains off. In one timing sequence, sweepingultrasound is activated when a pest is detected and one second later thestrobe flashes about five times in one half second. The sweepingultrasound remains on for an additional one and one-half seconds, thusthe deterrent event lasts a total of three seconds. The load is thenlocked out for a period of time to avoid continuous triggering or evenself-triggering, such as by the strobe being detected or electronicnoise emulating a triggering event.

[0013] In yet another embodiment, a high level of ultrasonic energy isproduced by using four ceramic speakers in a series-parallelconfiguration. Each speaker has a nominal input capacitance of about 0.2micro-Farads, and the four-speaker series-parallel also has a nominalinput capacitance of about 0.2 micro-Farads. This is approximately twicethe capacitance of conventional ultrasonic speakers, and achieves ahigher peak-to-peak resonant voltage on 12 V battery power or 18 V linepower, and over 120 dB of ultrasonic power.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a simplified block diagram of a pest deterrent apparatusaccording to an embodiment of the present invention;

[0015]FIG. 2 is a circuit diagram of a pest deterrent apparatusaccording to an embodiment of the present invention;

[0016]FIG. 3 is a simplified representative time line illustrating apest deterrent process according to an embodiment of the presentinvention;

[0017]FIG. 4 is a simplified flow chart of a pest deterrent processaccording to an embodiment of the present invention;

[0018]FIG. 5 is a simplified flow chart of a pest deterrent processaccording to another embodiment of the present invention;

[0019]FIG. 6 is a simplified flow chart of a triggering processaccording to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present invention provides an ultrasonic pest deterrent.Various operating conditions can be selected depending on the type ofpower source available (e.g. line power or battery operation), and theultrasonic deterrent signal can be combined with a flashing light forenhanced deterrent effect. In one embodiment, the ultrasonic signal isinitiated when a pest, such as a deer or dog, is detected. A selectedperiod of time lapses before the flash is discharged, thus ultrasounddraws the attention of the pest in the direction of the device, and theflash startles the pest. In a particular embodiment, the ultrasonicsound is generated with a microprocessor and the low-frequency flashoscillator AM modulates the ultrasound signal to produce sidebands ofultrasonic signal down to some frequencies within the range of normalhuman hearing but at much lower levels. This allows an operator toverify that the device is activated and the speakers are on.

[0021] I. An Exemplary Pest Deterrent Device

[0022]FIG. 1 is a simplified block diagram of an ultrasonic pestdeterrent device 10 according to an embodiment of the present invention.A sensor 12, such as a passive infrared (“PIR) sensor is aimed at thelocation where a pest is expected. Alternative sensing devices, such asDoppler radar devices, could be used. The output of the sensor 12 isprovided to a microcontroller 14, which generates the ultrasonic signalthat drives the speakers 16 and triggers the strobe or flash unit 19, ifselected, which includes the bulb 18 and drive circuitry 21. Power tothe unit can be supplied by either batteries 13 or line power 15. Thepower source can be automatically or manually selected with a switch 11.Line power is stepped down using conventional power supply techniques.

[0023] Sensors typically have low output levels that are amplified withhigh-gain amplifiers 17. These amplifiers can pick up signals that arenot generated by the sensor, such as noise or fluctuations in thevoltage supplied to the sensor or circuit, and trigger device operation.In particular, when the ultrasonic output or strobe is activated, supplyvoltage fluctuations, and ground current feedback can cause unintendedtriggering. A lockout circuit 20 prevents the device from continuouslytriggering if the pest dwells in the target area or if false triggeringevents occur, and allows the amplifiers to settle in anticipation ofanother signal from the sensor.

[0024]FIG. 2 is an exemplary circuit diagram for a pest deterrent device24 according to an embodiment of the present invention. Those of skillin the art will appreciate that many alternative circuits andimplementations of circuit functions are possible. The sensor 12 is adual-element PIR sensor that produces positive and negative pulses onthe output 13 when motion is detected. The PIR is decoupled from theregulated 5 V power IC2 by a 20 k-ohm series resistor R50 and 1000micro-Farad filter capacitor C41.

[0025] This decoupling and filtering stabilizes the regulated voltage tothe PIR and allows the PIR to function even in the event the batteriesare producing a lowered voltage, even as low as about 3 volts in someinstances. The voltage regulator IC2 provides the unregulated inputvoltage 29 to the output 27 if the input voltage drops below theregulated voltage. There is only about a 0.1 V drop through theregulator, so if the battery voltage drops below about 5.1 volts, thePIR can still function. This is to maintain functions with lowbatteries.

[0026] The pulse train from the sensor is inputted to the amplifierIC1C, which inverts and amplifies the signal. A 0.1 micro-Faradcapacitor C16 in combination with a 1 M ohm resistor R27 sets the gainand the low-frequency bandwidth limit for the detection circuit. The PIRhas a relatively low-frequency response, so the amplifier bandwidth isset to about 0.25-10 Hz. This keeps undesirable higher-frequencysignals, such as might arise from turning a load on or off, fromtriggering the circuit.

[0027] The output from the first amplifier IC1C drives the second stageamplifier IC1B, which again inverts and further amplifies the signalfrom the PIR and outputs to a comparator IC1A. Though the output of thesecond stage amplifier IC1B swings both positive and negative, only thepositive excursion (which is subsequently inverted in IC1A) is detectedfor triggering purposes. This is achieved according to the programmingof the microcontroller 14, which is programmed to only activate the load(sound and flash) if an appropriate negative voltage is provided to thetrigger input 25. This frees the negative output from IC1B to provide alock-out function. A quad operational amplifier, such as a model LP324M™available from NATIONAL SEMICONDUCTOR is used to implement thecomparators IC1A, and the amplifiers IC1C and IC1B.

[0028] When a positive excursion from the second stage amplifier IC1B isdetected, the comparator IC1A swings negative to turn on the load (i.e.to activate the ultrasound and strobe, if selected). This negative swingis fed back through a 2.2 micro-Farad feedback capacitor C20 through aseries resistor R32 to the summing junction 26, which is the negativeinput of the second stage amplifier IC1B. This negative signal providedto the negative input pulls the output of the second stage amplifierIC1B further up towards saturation, providing positive feedback. Thesaturation condition is held until the summing junction voltage iscompensated through the feedback resistor R31 (i.e. until the feedbackcapacitor C20 is sufficiently charged through R31 to pull the secondstage amplifier back from saturation).

[0029] After the feedback capacitor C20 is fully charged, the summingjunction returns to a quiescent state, which switches the output of thesecond comparator IC1A positive. This positive swing is again fed backthrough the feedback capacitor C20 and the series resistor R32 to thesumming junction 26, which causes the output of the second stageamplifier IC1B to swing to negative saturation because of the positivefeedback, essentially disabling the triggering operation. The load isnow off and the second stage amplifier IC1B cannot trigger the load tocome on again until the feedback capacitor C20 is discharged through thefeedback resistor R31. Thus, the circuit acts as a timer for determininghow long triggering is locked out after the load is turned off, andprovides a selected, positive, load on gate, trigger signal to themicrocontroller 14.

[0030] In one embodiment, the time the load is kept on is controlledaccording to the microprocessor programming. In other words, uponreceiving a trigger input of the proper polarity, the microcontrollerturns on the load for a selected period of time, such as about threeseconds. In another embodiment, the microcontroller or other circuitryactivates the load as long as the trigger signal has the proper polarityand is above a threshold voltage, for example, as long at the triggersignal is a negative voltage. In one embodiment a three-second-timeconstant is chosen for the lock out period; however, the lock out perioddoes not have to equal or even be close to the load-on period. It isgenerally desirable that the lock out period hold off the triggeringcircuit long enough after the load is turned off so that fluctuations inthe supply voltage, ground potential, or even light from the strobe orother non-pest input to the sensor, does not create a false trigger. Ifthe load-on period is determined by the duration of the trigger inputsignal (i e. R31-C20 time constant), a different lock-out period couldbe obtained by placing a diode and resistor in parallel to each other,the parallel combination being placed in series in the feedback path. Asdescribed above, the output of the second stage amplifier can swing bothpositive and negative, so the feedback capacitor C20 should be anon-polarized capacitor.

[0031] The lock out or hold off time after the load goes off insuresthat the power supplies and the motion sensor signal amplifiers have allsettled before motion detection is turned back on. The lock out periodalso eliminates continuous motion detection and extends battery-operatedlifetime. The 10 k-ohm series resistor R32, which is placed close to thesumming junction 26 on the printed circuit board, isolates the summingjunction from noise that might be picked up on the traces between theseries resistor R32 and the trigger input 25. This resistor has littleeffect on timing because it is much smaller than the 470 k-ohm feedbackresistor R31.

[0032] The pest deterrent device can operate in a variety of modes. Apower switch SW1A-SW1D allows the user to select between a high-powermode or a low-power mode. A bayonet plug connector V1 further selectsbetween battery operation or line-voltage operation using an 18 V DCadaptor input from a 115 V line supply. Plugging in the male bayonetplug automatically switches out the batteries and provides a controlsignal to the microprocessor 14 to switch from battery-operated mode toline power mode.

[0033] The unit operates at 100% load duty cycle in high power mode,enabling the load only when motion is detected (for the 3-second on,3-second lockout periods). In high-power battery operated mode, thesix-volt batteries B1, B2 are connected in series to provide twelvevolts to the circuit. When high-power mode is selected and the device isrunning on battery power, the unit operates at 100% duty cycle, onlyenabling the load when motion is detected. In high power mode using thepower adaptor from line power, the unit continuously emits ultrasound,with a change in the ultrasound when motion is detected. In low-powerbattery operation, the unit operates at 50% duty cycle, with the twobatteries connected in parallel to provide 6V to the circuit. Thisimproves battery lifetime, but produces lower ultrasonic power. The loadis cycled on and off at a frequency of about 20 Hz. In low-poweroperation running on line power, the unit operates at 50% duty cycleemitting a continuous noise, with a change in the ultrasound when motionis detected.

[0034] A sound switch SW3A-SW3C allows selection between a partiallyaudible (to humans) low ultrasonic mode output and a high ultrasonicmode output. In low ultrasonic mode on battery power, when motion isdetected, the unit sweeps from 15 kHz to 25 kHz once per second for 3seconds. The sweep is not a continuous sweep, but is carried out in aseries of eight steps. Different sweeps or steps could be used, and thesweep could be generated by an analog circuit in alternativeembodiments. Similarly, the ultrasonic signal could be produced by anexternal oscillator or other device that is controlled by themicrocontroller or other control circuitry.

[0035] Experiments with mice were conducted to evaluate theeffectiveness of a single, continuous ultrasonic tone versus thestepwise swept signal. From these observations it is believed thatchanges in the ultrasonic signal is a more effective deterrent than acontinuous tone. The microprocessor 14 is programmed to generate theultrasonic signal directly, which is amplified to drive the speakers.The microcontroller has sufficient bandwidth to generate ultrasonicfrequencies. In one embodiment the microcontroller is a custom-maskedmicrocontroller with 128 bytes of random access memory (“RAM) using a 4MHz crystal-controlled oscillator for the clock. Other types ofmicrocontrollers could be used, such as microcontrollers with integratedflash memory or programmable read-only memory (“PROM”) programmed withthe operating code, or the microcontroller can interface with anexternal memory chip or module that has been programmed to configure themicrocontroller to operate in the desired fashion. Other types of clocksor other clock frequencies compatible with the microcontroller andsufficiently high for direct generation of the highest desiredultrasonic frequency could be used if the microcontroller generates theultrasound.

[0036] A flash select switch SW2A turns the flash on or off according toa control signal (in this case ground or open) supplied to themicrocontroller. The flash can be enabled in any mode. A 20 kHz flashoscillator 28 charges the 2.2 micro-Farad, 250 V flash capacitor C27 and0.047 micro-Farad 200 V flash trigger capacitor C26 until sufficientvoltage is reached to discharge the strobe tube 30. The strobe flashesfive times in about one half second, according to the time constant ofthe flash trigger capacitor C26 and 3.3 M-ohm series resistor R40. Inlow ultrasonic mode, the flash oscillator is connected to the ultrasonicoutput through a 2 k-ohm series resistor R54 and 0.1 micro-Farad Faradseries capacitor C30, and further modulates the output signal providedto the speakers by modulating the gate voltage of amplifying transistorQ1. The amplitude modulation produces sidebands above and below theultrasonic frequencies being generated and some within the audiblerange. This audible portion of the output can be used to verify that theunit is on and operational. Furthermore, it is believed that the noisegenerated by the amplitude modulation makes the sound emitted by thespeakers more disagreeable to pests, thus improving the effectiveness ofthe pest deterrent.

[0037] In low ultrasonic mode on line power, the unit continuouslygenerates a signal switching between 17 kHz and 18 kHz at a rate ofabout 20 Hz. When motion is detected, the unit step-wise sweeps from 15kHz to 25 kHz once a second for about 3 seconds. After the 3-secondsweep period, the unit returns to the quiescent state of alternatingbetween 17 kHz and 18 kHz at a rate of 20 Hz until another trigger fromthe sensor enables the load (i.e. another triggering event after thelock-out period).

[0038] In high ultrasonic mode running on batteries, the unit sweepsfrom about 25 kHz to 40 kHz once per second for three seconds. Someanimals do not respond to the high end of this range, and in otherembodiments, the unit steps from 24-25 kHz, or 20-30 kHz. Other rangesand step sizes may be selected. In another embodiment, using line power,the unit continuously generates a signal switching between 31 kHz and 32kHz until motion is detected. When motion is detected, the unit sweepsfrom 25 kHz to 38 kHz (or other range) for three seconds, and thenreturns to alternating between 31 kHz and 32 kHz.

[0039] II. Operation of the Flash Circuit and Duty Cycle

[0040] When the flash is selected, the strobe flashes five times forhalf a second starting one second after motion is detected. Thus, assoon as motion is detected the ultrasonic signal is generated or changesfrom a quiescent state (e.g. alternating 17/18 kHz or 31/32 kHz), butthe flash does not strobe until the sound has been on for about onesecond. This provides an opportunity for the pest to direct itsattention at the device before the flash comes on. It is believed thatthis combination of sound and flashing light with an intervening periodis a more effective deterrent than if the flash started concurrentlywith the sound because the pest would not have an opportunity to look atthe device before the flash started.

[0041] If the unit is in low ultrasound mode, a further advantage isobtained from the amplitude modulation of the low ultrasound signal bythe flash oscillator. Namely, when the flash oscillator is enabled, anadditional change in the sound output occurs as the AM sidebands areproduced. This produces a very disturbing sound from as low as about 4kHz to over 30 kHz that occurs during, and as a function of, strobing.

[0042] The flash oscillator transistor Q7 uses feedback from thetransformer XF1. The high voltage output of the transformer XF1 isrectified by the diode D5 and charges the flash capacitor C27. As theflash capacitor charges, the flash trigger capacitor C26 also chargesthrough the resistor R40. The flash trigger capacitor C26 is in serieswith the trigger transformer L1. When the voltage at the cathode K ofthe programmable uni-junction transistor (“PUT”) 32 drops low enough,the PUT turns on, discharging the series capacitor C26 through thetrigger transformer L1. This current creates the trigger voltage to firethe flash and discharge the flash capacitor C27 through the strobe tube30. The flash capacitor C27 immediately starts re-charging, and thecycle starts over with the resistor R40 and series capacitor C26controlling the flash strobing rate. The flash oscillator 28 is turnedon and off by the microcontroller 14 through a flash control line 31.

[0043] When low-power operation is selected, the microcontroller 14generates a low-frequency square wave at the duty cycle output 34 todrive a bipolar transistor Q2 on and off. This transistor is in serieswith the ultrasonic output 36 of the microcontroller and the outputamplifier Q1. The edges of the square wave are rolled off by 1 k-ohmresistors R71, R72 in series with the base of Q1, and the 1 micro-Faradcapacitor C44 connected between a center node 38 of the resistors andground 40. The square wave edges are rolled off to prevent clicking inthe speakers as the ultra sound is gated on and off.

[0044] III. Output Driver and Speakers

[0045] The output amplifier Q1 is turned on and off by the ultrasonicoutput 36 from the microcontroller 14. External resistors R23, R24 allowchanging the high and low frequencies generated by the microcontrollerwithout having to re-program the microcontroller. The tapped inductor L2forms a resonant circuit with the speakers SP1, SP2, SP3, and SP4 toring them with a sine wave. The speakers are bi-morph ceramic speakerswith a frequency response from about 4 kHz up to about 40 kHz and areconnected in series-parallel. In other words, two sets of two parallelspeakers are connected in series. In the low range, the speakers areconnected across the entire center-tap inductor L2, while in the highrange the speakers are connected to the tap 42 of the inductor L2 for alower inductance. The switch SW3A, SW3B is a mechanical two-positionswitch, but electronic switching of the inductance could be done tobroaden the range of frequency sweeping using several inductors andtaps, or variably-tunable inductors could be used.

[0046] By connecting the speakers in a series-parallel configurationhigher output power is achieved. Each speaker has a capacitance of about0.2 micro-Farads, which is twice the capacitance used in a conventionalultrasonic speakers that typically have a capacitance of about 0.05-0.1micro-Farads. The series-parallel arrangement of the speakers provides acombined capacitance of 0.2 micro-Farads. This allows more current drawand more power to be drawn by the speakers, and more sonic power to bedirected at the pest. Similarly, while most speakers in conventionalultrasonic pest deterrent devices are driven at about 20V peak-to-peak,producing about 90-100 dB total sonic power, the present circuit,utilizing a combined total 0.2 micro-Farad speaker load and achievingabout 50 V peak-to-peak when in resonance with L1, produced over 120 dB.In another embodiment, the total ultrasonic output level was over about110 dB.

[0047] The ultrasonic output of a unit fabricated according to thepresent invention generated over 120 dB measured 18 inches from thespeakers at same ultrasonic frequencies. Not all the ultrasonic powercould be focused on the point of measurement, so it is believed that theactual ultrasonic output power is well over 120 dB. Using either a 12 Vbattery or 18 V line source also increases the power available to thespeakers over conventional 6 V or 12 V designs.

[0048] IV. An Exemplary Timeline and Methods

[0049]FIG. 3 is a representative timeline illustrating the operation ofa pest deterrent device with the flash enabled according to anembodiment of the present invention. The sensor detects the presence ofa pest at T0 and generates a series of alternating positive and negativepulses. Essentially instantaneously the ultrasound is turned on, iforiginally off, or changed to a sweep from an alternating tone,depending on the mode of operation. After one second T1, the flashflashes for about one-half second until T2, which is at 1.5 seconds. Thesweeping ultrasound remains on for an additional 1.5 seconds (threeseconds total) until T3. The sensor is than locked out of triggering theload for a period of about 2.5 seconds, allowing the trigger sensingamplifiers to settle after the load(s) is turned off, until T4, whichoccurs at 5.5 seconds. After the lock-out period the cycle can re-startif the sensor detects another or the same pest. These times are merelyexemplary.

[0050]FIG. 4 is a simplified flow chart of a pest deterrent process 400according to an embodiment of the present invention. A sensor generatesa pest detection signal (step 402) that initiates an ultrasonic signal(step 404) at a pest deterrent unit. After waiting a selected period oftime (step 406), for example about 1 second, a light flash(es) isgenerated (step 408) at the pest deterrent unit. In a further embodimentthe ultrasonic signal is amplitude modulated by the flash oscillatorsignal during the period the light is flashing (step 410). It isintended that the ultrasonic signal attracts the attention of the pestto the pest deterrent unit, and that the flash then startles the pest todrive it away.

[0051]FIG. 5 is a simplified flow chart of a pest deterrent process 500according to another embodiment of the present invention. A pestdeterrent unit produces a first ultrasonic output prior to motion beingdetected (step 502). For example, the unit could produce a continuoustone or alternating high-low tones. When motion is detected (step 504),the unit changes to a second ultrasonic output (step 506), such as aswept (frequency) ultrasonic signal, amplitude modulated ultrasonicsignal, or chopped (on/off) ultrasonic signal.

[0052]FIG. 6 is a simplified flow chart of a signal triggering process600 according to another embodiment of the present invention. Whenmovement occurs within the range of a motion sensor, the sensorgenerates a trigger signal having a first polarity (i.e. positive ornegative) (step 602). The trigger signal is provided to a saturatingamplifier (step 604) capable of producing a positive or a negativeoutput voltage and a load is activated (step 606). Positive feedback isprovided to the saturating amplifier to drive the amplifier to a firstsaturation voltage (step 608). Positive feedback from the firstsaturation voltage is provided through an inverter and a feedbackcapacitor to a summing junction input of the saturating amplifier andnegative feedback from the output of the saturating amplifier isprovided to the summing junction through a feedback resistor (step 610),which discharges the feedback capacitor at a first selected rate.

[0053] After a selected period of time, the voltage at the summingjunction drops below a first threshold voltage and the saturatingamplifier provides a second saturation voltage having the oppositepolarity from the first saturation voltage (step 612). The load, whichis only enabled if a signal with the first polarity is detected, isde-activated (step 614). Positive feedback from the second saturationvoltage is provided through the inverter and the feedback capacitor tothe summing junction input of the saturating amplifier, and negativefeedback is provided from the output of the saturation amplifier to thesumming junction input through the feedback resistor to discharge thefeedback capacitor at a second selected rate (step 616), wherein asecond trigger signal will not activate the load until after the load isde-activated and the voltage at the summing junction drops below asecond threshold voltage. The term “below” relates to the absolute valueof the voltage(s) at the summing junction.

[0054] The rate of compensation in one embodiment is essentially equal,that is, the high and low saturation voltages have about the samemagnitude and only a feedback resistor is used to couple negativefeedback to the summing junction. In an alternative embodiment, thesaturation voltages might not be symmetrical, and in yet otherembodiments, a diode (or diode with a series resistor) can be placed inparallel between the output of the saturating amplifier and the summingjunction.

[0055] Although the present invention has been described with referenceto specific embodiments, modification and variation can be made withoutdeparting from the subject of the invention as defined in the followingclaims. For example, a sound detector, vibration detector, or radardetector might be used instead of a PIR as the pest detector. Further,the load, although described in specific embodiments as aseries-parallel combination of high-capacitance ceramic speakers couldbe other types of speakers or ultrasonic devices. Similarly, althoughspecific circuits with specific values of components have beendescribed, other circuits, component values, and types of devices couldbe used, such as by using analog circuits to provide some of thefunctionality of the microprocessor in certain embodiments.

We claim:
 1. A pest deterrent device comprising: a sensor capable ofdetecting a pest; a trigger circuit electrically coupled to the sensor,the trigger circuit providing a triggering signal having a firstpolarity in response to a triggering event, the trigger circuitactivating a load during the triggering signal, the triggering signalbeing coupled to a summing junction through a capacitor as positivefeedback; a negative feedback path electrically coupling an inversetriggering signal to the summing junction to discharge the capacitor andturn off the triggering signal and the load after a triggering period,the trigger circuit providing a lockout signal following the triggeringsignal, the lockout signal being coupled to the summing junction throughthe capacitor as positive feedback and an inverse lockout signal beingcoupled to the summing junction as negative feedback to lock out theload until the lockout signal is turned off after a lockout period. 2.The pest deterrent device of claim 1 wherein the sensor produces both apositive pulse and a negative pulse upon detection of a pest, only oneof the positive pulse or the negative pulse triggering the load.
 3. Thepest deterrent device of claim 1 wherein the trigger circuit includes afirst amplifier providing a first output and a second amplifierproviding a second output, the first output being the inverse triggeringsignal and being coupled to an inverting input of the second amplifier,the second output being the triggering signal.
 4. The pest deterrentdevice of claim 1 wherein the negative feedback path includes a resistorin parallel with a diode.
 5. The pest deterrent device of claim 4wherein the negative feedback path further includes a second resistor inseries with the diode and in parallel with the resistor.
 6. A pestdeterrent device comprising: a sensor capable of detecting a pest; atrigger circuit electrically coupled to the sensor, the trigger circuitproviding a triggering signal having a first polarity in response to atriggering event, the trigger circuit activating a load during thetriggering signal, the triggering signal being coupled from an output ofan inverting amplifier to a summing junction of a second invertingamplifier through a capacitor as positive feedback; a negative feedbackpath electrically coupling an inverse triggering signal from a secondoutput of the second inverting amplifier to the summing junction todischarge the capacitor and turn off the triggering signal and the load,the trigger circuit providing a lockout signal following the triggeringsignal, the lockout signal being coupled from the output of the firstinverting amplifier to the summing junction through the capacitor aspositive feedback and an inverse lockout signal being coupled from thesecond output of the second inverting amplifier to the summing junctionas negative feedback to lock out the load until the lockout signal isturned off.
 7. A method of locking out a detector circuit, the methodcomprising: providing a detection signal from the detector circuit to asaturation amplifier; producing a first saturated output signal from thesaturation amplifier, the first saturated output signal having a firstelectrical polarity; electrically coupling the first saturated outputsignal to an inverting input of a second amplifier; inverting the firstsaturated output signal to produce a triggering signal having a secondelectrical polarity and being configured to activate a load;electrically coupling the triggering signal through a capacitor to aninverting summing junction of the saturation amplifier; electricallycoupling the first saturated output signal to the inverting summingjunction of the saturation amplifier; discharging the inverting summingjunction to turn off the triggering signal and the load after a triggerperiod; producing a second saturated output signal from the saturationamplifier, the second saturated output signal having the secondelectrical polarity; inverting the second saturated output signal toproduce a lockout signal having the first electrical polarity and beingconfigured to de-activate the load; electrically coupling the lockoutsignal through the capacitor to the inverting summing junction of thesaturation amplifier; electrically coupling the second saturated outputsignal to the inverting summing junction of the saturation amplifier;discharging the inverting summing junction to turn off the lockoutsignal after a lockout period.
 8. The method of claim 7 wherein thelockout period is essentially equal to the trigger period.